The present invention relates to the diagnosis of cancer susceptibilities in subjects having a defect in the FANCD2 gene and the determination of suitable treatment protocols for those subjects who have developed cancer. Animal models with defects in the FANCD2 gene can be used to screen for therapeutic agents.
Fanconi Anemia (FA) is an autosomal recessive cancer susceptibility syndrome characterized by birth defects, bone marrow failure and cancer predisposition. Cells from FA patients display a characteristic hypersensitivity to agents that produce interstrand DNA crosslinks such as mitomycin C or diepoxybutane. FA patients develop several types of cancers including acute myeloid leukemias and cancers of the skin, gastrointestinal; and gynecological systems. The skin and gastrointestinal tumors are usually squamous cell carcinomas. At least 20% of patients with FA develop cancers. The average age of patients who develop cancer is 15 years for leukemia, 16 years for liver tumors, and 23 years for other tumors. (D'Andrea et al., Blood, (1997) Vol. 90, p. 1725, Garcia-Higuera et al., Curr. Opin. Hematol., (1999) Vol. 2, pp. 83-88 and Heijna et al., Am. J. Hum. Genet. Vol. 66, pp. 1540-1551).
FA is genetically heterogeneous. Somatic cell fusion studies have identified at least seven distinct complementation groups (Joenje et al., (1997) Am. J. Hum. Genet., Vol. 61, pp. 940-944 and Joenje et al., (2000) Am. J. Hum, Genet, Vol. 67, pp. 759-762). This observation has resulted in the hypothesis that the FA genes define a multicomponent pathway involved in cellular responses to DNA cross-links. Five of the FA genes (FANCA, FANCC, FANCE, FANCF and FANCG) have been cloned and the FANCA, FANCC and FANCG proteins have been shown to form a molecular complex with primarily nuclear localization. FANCC also localizes in the cytoplasm. Different FA proteins have few or no known sequence motifs with no strong homologs of the FANCA, FANCC, FANCE, FANCF, and FANCG proteins in non-vertebrate species. FANCF has weak homology of unknown significance to an E. coli RNA binding protein. The two most frequent complementation groups are FA-A and FA-C which together account for 75%-80% of FA patients. Multiple mutations have been recognized in the FANCA gene that span 80 kb and consists of at least 43 exons. FANCC has been found to have 14 exons and spans approximately 80 kb. A number of mutations in the FANCC gene have been identified which are correlated with FA of differing degrees of severity. FA-D has been identified as a distinct but rare complementation group. Although FA-D patients are phenotypically distinguishable from patients from other subtypes, the FA protein complex assembles normally in FA-D cells (Yamashita et al., (1998) P.N.A.S., Vol. 95, pp. 13085-13090).
The cloned FA proteins encode orphan proteins with no sequence similarity to each other or to other proteins in Germanic and no functional domains are apparent in the protein sequence. Little is known regarding the cellular or biochemical function of these proteins.
Diagnosis of FA is complicated by the wide variability in FA patient phenotype. Further confounding diagnosis, approximately 33% of patients with FA have no obvious congenital abnormalities. Moreover, existing diagnostic tests do not differentiate FA carriers from the general population. The problems associated with diagnosis are described in D'Andrea et al., (1997). Many cellular phenotypes have been reported in FA cells but the most consistent is hypersensitivity to bifunctional alkylating agents such as mitomycin C or diepoxybutane. These agents produce interstrand DNA cross-links (an important class of DNA damage).
Diagnosing cancer susceptibility is complicated because of the large number of regulatory genes and biochemical pathways that have been implicated in the formation of cancers. Different cancers depending on how they arise and the genetic lesions involved may determine how a subject responds to any particular therapeutic treatments. Genetic lesions that are associated with defective repair mechanisms may give rise to defective cell division and apoptosis which in turn may increase a patient's susceptibility to cancer. FA is a disease condition in which multiple pathological outcomes are associated with defective repair mechanisms in addition to cancer susceptibility.
An understanding of the molecular genetics and cell biology of Fanconi Anemia pathway can provide insights into prognosis, diagnosis and treatment of particular classes of cancers and conditions relating to defects in DNA repair mechanisms that arise in non-FA patients as well as FA patients.